1. Technical Field
The present invention relates to a sensor.
2. Related Art
A SAW (Surface Acoustic Wave) sensor, which uses a surface acoustic wave caused by the piezoelectric effect, is known. A SAW sensor converts a received signal into a surface acoustic wave propagating on a substrate of the SAW sensor, and again converts the surface acoustic wave, into a signal to be transmitted. A delay time of a transmitted signal depends on conditions such as a propagation distance of a surface acoustic wave or the material of a substrate of a SAW sensor, which can be affected by a change in the circumstance surrounding a SAW sensor. Therefore, measuring of a delay time of a transmitted signal makes it possible to distinguish plural SAW sensors, or to detect a change in the circumstances surrounding a SAW sensor.